Complicated vacuum extraction : focus on traction force

Abstract

Introduction: Vacuum extraction is a common operative vaginal delivery in the final stage of labor, and generally considered a safe alternative to emergency cesarean section. However, there is insufficient evidence regarding the causes of the rare but severe perinatal complications that may occur, such as intracranial or subgaleal hemorrhage, and possibly also asphyxia related encephalopathy. High levels of traction force and failed extraction are two suggested risk factors for adverse neonatal outcome. Therefore, the aims of this thesis were to investigate employed traction force, explore its capacity to predict a difficult extraction, and to evaluate its association to neonatal outcome. Another aim was to describe the rate of failed extraction and its associated risk factors, and to evaluate clinical team training as a tool to decrease failed extraction.

Methods and materials: The studies were mainly observational: descriptive or analytical. Although retrospective by design, the exposure data was registered prior to the outcome data, and the registrator of outcome data in study III and IV were blinded to the exposure. The population base consisted of women giving birth at Karolinska university hospital, Huddinge during the different study periods. General inclusion criteria for the majority of the studies were term, singleton pregnancy delivered by low and mid vacuum extraction. The descriptive traction force study (study II) included outlet extractions as well. For the traction force measurements in, an intelligent handle attached to a regular metal cup was used, while clinical data were acquired from electronic patient charts.

Results: In study I, we found a decreased incidence of failed extractions after implementation of a clinical team training program, RR 0,3-0,62, but no favorable effect on neonatal outcome. Study II showed higher maximum peak (momentary) force than previously reported, 452 Newton. The maximum total traction force (time force product), 1180 Newtonminutes, was confirmative of a previous metal cup study but exceeding plastic cup measurements. In study III, a diagnostic test using measured traction force for early prediction of heavy category extraction displayed a high negative predictive value (NPV 0,94), and was able to detect two thirds of heavy extractions (PPV 0,65). In study IV, we found a possible association between exposure to high level traction force and admission to the neonatal intensive care unit.

Conclusion: The traction force studies have added further details regarding the level of force employed, as well as discussions regarding possible safety limits. However, methodological limitations call for cautious interpretations. The diagnostic test of study III needs external validation, and the possible association between exposure to high level traction force and admission to the NICU may be biased by residual confounding. The evaluation of team training showed measurable effects on the rate of failed extractions, but no coincident improvement of neonatal outcome. An important strength is that we have shown that the intelligent handle is safe and well tolerated among users. Possible future areas to implement its use include pedagogical situations, feedback on high level traction force to the obstetrician, and objective documentation of the procedure.